Mercedes C class w204

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i860
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Mercedes C class w204

#1 Post by i860 » Thu Dec 06, 2018 9:52 am

Hi
First, thank you for accepting me on this forum.
I have a Mercedes C class 280 w204 m272,v6, 240hp from 2008 converted on lpg. Agis p13 obd can iso, barracuda injectors, kme gold reductor.
I have a few small problems and I really want to find the answer.
The car is running ok on lpg the stft and ltft are in the limits as per my pic1.
The first problem if enable the "obd on" option in the program pic 2 i have this error pic 3 ( the program is in demo mode not connected to the car ). Seems like am communication error is there something that I need to install to make the fuel pump not trigger this error?
If the obd is off then there is no error.

The second one ( i know what you gone say, don't use the option ) is related to the obd on + enable obd correction pic4. If this option is enable the lpg switch console will not go to sleep, the B button ( petrol ) is always on and overnight my battery will be drain. If the option is not enable the console will switch off after 1m when you take the key from the ignition.

And the last question
I did update the ECU software and the LTFT is changing like the STFT. Before the update the LTFT will not change as fast as in the video, have you seen this kind quick change of LTFT on others car?
https://www.youtube.com/watch?v=qnwHM-oUZzw

I attached the pics on this lnk
https://imgur.com/a/Pu8Jzrn
pic3
pic1
pic2
pic4

LPGC
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Re: Mercedes C class w204

#2 Post by LPGC » Thu Dec 06, 2018 10:38 am

No time to watch videos etc this morning but seems to me you've explained enough in words to know what's going on.

Don't connect to OBD, especially not on a Merc. The connection interferes with the vehicle canbus and can cause all sorts of problems due to preventing the vehicle's various ECU's talking to each other (or at least messing up some time critical canbus interactions). For example, can stop the engine ECU talking to autobox ECU properly leading to harsh auto gear changes, can even prevent the engine starting as it interferes with the engine ECU coms with the body/immobiliser ECU. I know of a few people who started to suffer some of these symptoms so drove around with a scanner plugged into the OBD socket trying to trace the problem -when I told them to unplug the scanner all the problems went away!

Fuel pump error could be actual when running on LPG, in which case it would probably be because the car needs a fuel return fitting (I'd have to check on this but lots of 2008 Mercs do need a fuel return fitting - and unless one is fitted you stand no chance of calibrating the LPG system properly). Or, could be another canbus issue, fuel pump control module might not be able to communicate properly with the Bcm/Petrol Ecu with the LPG ECU or a scantool connected to OBD... Ironic that in the case of the scantool it's checking for problems that can cause a problem! Or, could be an actual fuel pump, pump control module or fuel pressure issue.

The OBD connection can also keep ECU's awake - when the petrol ECU gets a canbus signal it powers up the engine's positive feed (to injectors, coil packs, etc), which if the LPG ECU is wired in the usual way to sense ignition on from petrol injector positive keeps the LPG ECU awake, then you get the latched condition of petrol ECU and LPG ECU keeping each other awake. You can usually prevent this problem by wiring the LPG ECU ignition on wire not to petrol injector positive but to something else that might only be live when ignition is on (such as maybe a fag lighter socket). In light of the above problems though, which this won't fix, this doesn't really matter because you won't want to connect to OBD anyway.

If Stft max/mins out (say +25% / -25%) the petrol ECU sees this as a fault condition and won't steer Ltfts. But if stfts were/are all good running on LPG there could be another issue preventing ltft steering and might guess that a couple of such issues would be if a canbus fault or fuel pump fault is detected.
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i860
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Re: Mercedes C class w204

#3 Post by i860 » Thu Dec 06, 2018 11:50 am

Hi, thank you for taking the time to read my post.
The w204 is my wife daily car so I am not playing as much as on my car but I monitor LTFT very often. With the engine, off and ignition on I can read it properly.
Also if i was needing a return you said i will not be able to calibrate correctly, as you can see my ltft is ok on both banks.

I have a Mercedes slk 350 on lpg, same lpg ecu same injectors.
This is on obd on + enable correction since 3 years and no problems, as i play a lot with this car. The only problem is when scanning the car I have to disable obd from the lpg ecu.
Also, I install a fancy lpg switch so I don't have to plug any obd tool to read the stft and ltft.
https://www.youtube.com/watch?v=3m0DmWfitGs

I know a lot of people don't like the auto correction but in my case, on slk 350 I found this option ok.
I dyno the car on petrol, LPG with correction off and lpg with correction on. With obd correction off I was 9hp down comparing to petrol and with obd on I was 5hp down comparing to petrol.

LPGC
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Re: Mercedes C class w204

#4 Post by LPGC » Thu Dec 06, 2018 3:14 pm

The canbus problems I referred to will only occur on certain affected Merc models, good if they don't occur on the SLK but maybe they are occurring on the C class. You have to disable the LPG OBD connection to read trims with a scan tool because the LPG OBD connection is extra traffic on the canbus, the extra traffic can cause problems on some Mercs of vehicle ECU's not being able to communicate with each other properly.

On your SLK, if the system was calibrated properly there's no reason why it should make any less power than with OBD connection enabled.

How do you read LTFT's with engine off and ignition on?

Still haven't watched any of your vids, will when I get time, but can imagine what the content.
Full time LPG installer
Servicing / Diagnostics / Repairs to all systems / DIY conversion kits supplied with thorough tech support
Mid Yorkshire
2 miles A1, 8 miles M62,
http://www.Lpgc.co.uk
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07816237240

i860
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Posts: 4
Joined: Thu Dec 06, 2018 9:19 am

Re: Mercedes C class w204

#5 Post by i860 » Thu Dec 06, 2018 8:26 pm

Hi
For reading ltft on w204 i use an elm327 with android phone.
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